The present invention is directed to motor vehicle restraint systems, and more particularly to apparatus for detecting and characterizing a frontal impact of the vehicle.
Motor vehicle restraint systems have become increasingly complex, and often include a number of different restraint devices (such as seat belt pre-tensioners, frontal air bags, knee bolsters, and so on) designed to protect the occupants under a variety of circumstances. For this reason, it is important to be able to reliably characterize a detected impact or crash event in order to select the most appropriate restraints, and to deploy the selected restraints at the optimal time. A common approach in this regard is to install crash sensors at distributed locations of the vehicle, and to process all of the crash sensor data for purposes of characterizing a detected crash event. Also, various types of crash sensors can be used, such as mechanical inertia and intrusion switches, electronic accelerometers, piezoelectric strips, and so on. From a practical standpoint, however, only a limited number of crash sensors are typically used, so that the system cost and data processing requirements might be minimized. Thus, what is needed is a cost-effective way of detecting and characterizing frontal vehicle impacts.
The present invention is directed to an improved and cost-effective sensing apparatus for quickly and reliably characterizing frontal impacts with only minimal data processing requirements. According to this invention, two or more longitudinally displaced piezoelectric strips strategically located in a frontal portion of the vehicle produce impact signals that are analyzed to characterize the type of impact and the structural crush rate. In a simple implementation involving only two piezoelectric strips, a first strip extends laterally along a forward portion of the front bumper, and a second strip extends laterally along a forward portion of the hood panel, above and rearward of the first strip. In cases where an impact signal is developed by only one of the two strips, a high (under-ride) or low (over-ride) impact is indicated. If significant impact signals are developed by both strips, the intervening time is measured as an indication of the structural crush rate. In a more complex implementation, the bumper and hood strips are divided into two or more individual strip segments so the center and distribution of impact and the impact vector may be quickly and reliably characterized as well.